新疆东准噶尔克拉麦里蛇绿岩地球化学:洋脊俯冲的产物  

Geochemical characteristics of Karamaili ophiolite in east Junggar, Xingjiang: products of ridge subduction.

作　　者：刘希军[1] 许继峰[1] 侯青叶[1] 白正华[1] 雷敏[2] 

机构地区：[1]中国科学院广州地球化学研究所同位素年代学和地球化学重点实验室 [2]中国地质大学地球科学与资源学院,北京100083

出　　处：《岩石学报》2007年第7期1591-1602,共12页Acta Petrologica Sinica

基　　金：国家杰出青年基金项目(40425003)资助.

摘　　要：新疆东准噶尔克拉麦里蛇绿岩中的镁铁质岩兼具有洋中脊玄武岩(MORB)和岛弧拉斑玄武岩(IAB)的特征,岩石地球化学特征表现为轻稀土(LREE)亏损、平坦或略微富集,不同程度地亏损高场强元素(HFSE)而富集大离子亲石元素(LILE),成分上非常相似于受洋脊俯冲影响的 Chile Ridge 和 Cocos Ridge 玄武岩。可以认为其可能形成于受洋脊俯冲影响的岛弧或弧前扩张环境。相对较高的ε_(Nd)(t)(7.2～9.8)、低 Nb/Zr、Ta/Yb 比值,说明在洋脊俯冲的影响下,其源区可能存在有至少三种组分:弧下地幔、来自消减板片流体和俯冲沉积物、MORB 地幔。The marie rocks of Karamaili ophiolite in East Junggar of Xinjiang province show both compositional characteristics of a mid-ocean ridge basalt（MORB） and an island-arc basalt （IAB）. They display flat to light rare earth element （REE）-depleted and slight enriched patterns. The spider diagrams for trace elements indicate that they are variable depleted in high filed-strength elements （HFSE）, but enriched in large ion lithophile elements（LILE）. The composition characters of these marie rocks are much similar to those of the Chile Ridge and Cocos Ridge basalts, which are typically affected by ridge subduction. Discrimination diagrams demonstrate that mafic rocks of the Karamaili ophiolite plot within the arc and MORB filed, and show a transitional composition from lAB to MORB, therefore the ophiolite was possibly formed in a subducted ridge-affected island arc or forearc setting. Relatively high εNd （t）values （7.2 -9. 8） and low Nb/Zr,Ta/Yb ratios suggest that at least three components were involved in their source： sub-arc depleted mantle; fluids dehydrated from the subducted slab and marine sediment and MORB mantle.

关 键 词：准噶尔 克拉麦里 蛇绿岩 洋脊俯冲 弧前环境 

分 类 号：P588.125[天文地球—岩石学]